The Blue Shark is a species of shark found almost everywhere in the world and is the most widely distributed shark species. It is one of the most easily recognizable sharks because of their distinct blue coloration – a combination of deep indigo and vibrant blue. The shark species plays an important role in ocean ecosystems.
Blue Shark Scientific Classification
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Size: Males and females show sexual dimorphism with the female being larger than the male. They can grow up to 3.8 meters (12 ft). But usually, the length of the males is between 1.82 and 2.82 m (6.0 to 9.3 ft), whereas for the female, it is 2.2 to 3.3 m (7.2 to 10.8 ft).
Weight: Males typically weigh between 27 and 55 kg (60 to 121 lb) while larger females between 93 and 182 kg (205 to 401 lb).
Body Anatomy/Skin Coloration: Blue sharks are literally blue in color. While the dorsal (back) side is a distinct deep blue, the ventral part (underbelly) is white. Both the sides are bright blue.
Eyes: Large round eyes that seem to be completely black from a distance.
Nose: Nostrils are situated just in front of the eyes, under the snout.
Teeth/Dentition: The upper and the lower jaws have rows of very sharp teeth, adapted to tear their prey quickly.
The lifespan of this fish is up to 20 years in the wild, and around 8 in captivity.
The blue sharks are found in the coastal waters of all the continents except Antarctica. It dwells temperate, tropical and subtropical waters up to 350 meters deep. It lives near the coasts except those of Antarctica. Currently, no regional subspecies of this shark has been classified.
Habitat: Where do Blue Sharks live
The species inhabits in the tropical, subtropical and temperate waters up to 350 meters deep. They prefer water between 7° and 16°C.
Blue sharks are nomadic animals that can migrate over long distances in search of food or for mating. In general, these sharks are lethargic and slow swimmers, and would only increase their moving speed when they get stimulated by other factors including views of other underwater animals that can be their prey. In such cases, the blue shark can prove to be one of the fastest-moving fish. They communicate with each other through movement gestures or body language. No other data about communication is available.
They have also been reported to perform acrobatics out of the water surface while chasing prey. The sharks are social in nature and move in small to medium size schools. There is also clear evidence of hierarchy in a group that is usually determined by size, sex, etc. However, all-male or all-female groups have also been seen. They are curious and fancy approaching the shores and are often seen by divers and boats.
Diet: What Do Blue Sharks Eat
They are carnivorous, opportunistic predators feeding on about 24 species of cephalopods and 16 species of fish. Their diet includes squids, octopuses, lobsters, crabs, small sharks, and occasionally seabirds. Various fishes like haddock, pollock, flounders, mackerel, herring, sea raven, silver hake, white hake, red hake, butterfish, and cod are also common.
Reproduction & Life Cycle
These creatures are polygamous and reproduce through viviparity after they attain the age of sexual maturity when they are around 5 to 6 years old. Before mating, the male blue shark would induce a bite between the first and the second dorsal fin of the female. If the latter accepts the courtship, the former would insert its clasper inside the oviduct of the female. This act delivers the sperm for the fertilization of the eggs. When the mating is done, both sharks part ways and never join again.
The female migrates northward for delivering the offspring, though it is not yet known how frequently the females give birth, or how long the sperm is stored inside the oviduct. The gestation period of the female is 9 to 12 months, while the young ones are hatched inside their mother’s body, after which the female gives birth to live young. A single litter can contain anything between 4 and 130 pups, with the average range being 25 to 50.
The baby blue sharks do not get any parental care after they are born. The mother shark leaves the juveniles soon after they are released from its body. Interestingly, these sharks have one of the fastest rates of growth among all shark species. A baby shark can keep growing up to 30 cm every year until they eventually reach the age of maturity.
- The contrast in colors (dark and bright blues contrasted with white underside) is called ‘countershading’ that helps them camouflage in the open waters.
- The conical snout of these fish is very long (in fact, longer than even the full breadth of its mouth). This feature gives them master speed while chasing fast-moving prey including squid and various cephalopods.
- The electroreceptors called ‘Ampullae of Lorenzini’, situated just below its snout, aid them in catching electrical fields that are generated from the contraction of muscles of their prey.
- The shark also has a unique sense of smell (like blood, or of any particular species), which again help them locate prey in deep water.
- The skin of the female is 3 times thicker than the male. This is to withstand the aggressive bite of the male during mating.
Usually, the young ones are frequently eaten by larger shark species that share a common range including the great white and the tiger sharks. However, both juveniles and adults are sometimes killed by seals and sea lions that eat just their liver and stomach.
The adult blue sharks are often infested by certain parasites (like tapeworms), which usually come from other infected prey like opah, longnose lancetfish, etc.
Owing to poaching and illegal fishing, the blue shark population is gradually going down. It is estimated that 10 to 20 million of them are killed each year for consumption and other purposes. The IUCN 3.1 has categorized this species under the ‘NT’ (Near Threatened) species list.
- In 1758, naturalist Carl Linnaeus named this creature Prionace glauca, wherein the generic name was derived from ‘prion’ and ‘akis’, which in Greek mean ‘saw’ and ‘point’, respectively (indicative of their saw-like teeth and pointed snout). The term ‘glauca’ too comes from a Greek word ‘glaukos’, which means ‘bluish gray’.
- Almost 15 to 20 million blue sharks are killed every year.
- These sharks have an unaffected relationship with humans, and practically pose no threat towards them since they seldom bite divers. Only 13 incidents of blue shark biting have been recorded between 1580 and 2013, out of which, only four proved to be fatal.
- Since these sharks are often seen moving in groups, they are also called ‘the wolves of the sea’.
- A two-headed baby blue shark pup was found by fishermen from inside the belly of its mother with each head possessing an independent set of teeth and eyes. Scientists explained this as the same case as Siamese twins.